Presently, inadvertent dust formation is a major problem facing many known techniques of thin film crystal growth that involve a gas or vapor phase reactant, including chemical vapor deposition (CVD) methods, such as metalorganic chemical vapor deposition (MOCVD), plasma enhanced chemical vapor deposition (PECVD), and remote plasma enhanced chemical vapor deposition (RPECVD), and physical forms of thin film deposition such as reactive sputtering and reactive evaporation.
Similarly, HVPE (sometimes called hydride vapor phase epitaxy or halide vapor phase epitaxy) can be affected by dust formation. Dust formation occurs when reactions take place in the gas phase between the reacting species, instead of on the surfaces of the “substrates” on which the films are intentionally grown. Molecules formed in the gas phase coalesce into larger dust particles. Dust formation is often the result of parasitic gas phase reactions and is an unwanted effect during thin film growth. Dust formation can cause dust to build up on the walls of a reaction chamber so that the reactor chamber eventually requires down time for cleaning. In severe cases the dust can be incorporated in the film itself, or no film may grow because dust formation is entirely prevalent.
There are some known techniques to attempt to reduce the formation of such parasitic dust by suppressing the gas phase reactions that lead to dust formation. For example by chemical means, although chemical techniques that suppress parasitic gas phase reactions can have the unwanted effect of also suppressing the reactions that cause film growth on a substrate. Another means of attempting to suppress dust formation is to reduce the density of the reacting species in the gas phase of a film growth region. This is done so that the individual molecules or other reacting species are less likely to collide with one and other and undergo a chemical interaction before reaching the substrate, though this can have the unwanted effect of lowering the film growth rate. It may also be possible to lower the temperature of the gas so that parasitic reactions in the gas phase are less prevalent, but this is not always easily achieved above a heated substrate, or with plasma heating present.
For the film growth techniques of PECVD and RPECVD, in particular, it has been observed by the inventor that the high delivery rates for reactant species that would otherwise lead to high growth rates is not possible due to severe dust formation. Hence these known techniques are limited in terms of their potential film growth rates.
There is thus a need for a method and/or device that addresses or at least ameliorates one or more problems inherent in current systems and methods.
The reference in this specification to any prior publication (or information derived from the prior publication), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from the prior publication) or known matter forms part of the common general knowledge in the field of endeavor to which this specification relates.